This application claims the benefit of Japanese Patent Application P2001-177, 994, filed on Jun. 13, 2001, the entirety of which is incorporated by reference.
1. Field of the Invention
The invention relates to a process for producing an optical waveguide, which may be preferably used as a device for generating second harmonic wave of quasi-phase matched system and optical modulator.
2. Related Art Statement
Recently, it has been studied to develop a device for light modulation by forming an optical waveguide in various kinds of materials. Such devices are used in systems for optical communication. The so-called ridge shaped optical waveguides have been expected as optical modulators, optical switching devices or the like. It is proposed a Quasi-phase matched (QPM) type second harmonic generation (SHG) device using an optical waveguide made of a lithium niobate or lithium tantalate single crystal, in which a periodically reversed polarization structure is formed. Such SHG device has been expected as a blue laser light source to be used for light pickups. The second harmonic generation devices find a wide range of applications such as optical disc memorization, medical uses, optochemical uses, various optical measurements, etc.
Japanese patent laid-open publication (Kokai) A269,430/1997 discloses a process of producing a ridge-shaped optical waveguide used for a device for generating a second harmonic wave. The waveguide is formed by subjecting an oxide single crystal to abrasion working using an excimer laser. Such oxide single crystal includes lithium niobate and a lithium niobate-lithium tantalate solid solution.
The inventors have further studied the above process and found the following problems. That is, after a substrate comprising, for example, lithium niobate single crystal is subjected to laser working using an excimer laser to form an optical waveguide, they irradiated coherent light into the resulting optical waveguide. They found that a part of the coherent light may be scattered from the surface of the optical waveguide, resulting in optical loss.
It is an object of the invention is to provide a method for producing an optical waveguide by irradiating a laser ray onto a substrate made of an oxide single crystal so that the scattering of light from the surface of the optical waveguide may be prevented when light is transmitted through the waveguide.
The invention provides a method for producing an optical waveguide, the method including the steps of:
irradiating a laser beam onto an oxide single crystal material so that the material is worked by the laser beam to form an optical waveguide portion having a laser working face; and
subjecting the laser working face to a wet etching treatment to provide an optical waveguide.
The invention further provides an optical waveguide produced by the above method.
The invention further provides a frequency converting device of quasi-phase-matched system, including:
an optical waveguide produced by the method; and
a periodically reversed polarization structure formed in the optical waveguide.
The inventors have studied the cause of the scattering of light from the surface of the optical waveguide when transmitting light through the waveguide, and found the followings. That is, a kind of microscopic product as a result of the laser working (referred to as xe2x80x9cworking productxe2x80x9d) is adhered on the surface of the waveguide formed by laser ablation working, resulting in the scattering of light on the interface between the working product and the surface of the waveguide.
The scattering of light along the interface between the working product and waveguide means that the refractive indexes of the working product and the oxide single crystal constituting the waveguide are different with each other. It is considered that the material of the working product is different from the oxide single crystal constituting the waveguide, based on the difference of the refractive indexes.
The inventors have then studied, based on the above findings, a process for selectively removing the working product and preventing the introduction of roughness on the surface of the optical waveguide. They finally found that a wet etching treatment under a condition for removing the working product is effective for removing the working product without introducing the excessive roughness or deficiencies on the surface of the optical waveguide. The scattering of light on the surface of the waveguide may be thus prevented.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.